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Cvhe chiller giving a prestart alarm of "Differential Oil Pressure Overdue". This has happened almost consistently since the warm weather has started and the chiller has been on line. To this point I have attempted to cycle on the oil pump via the service test mode. The oil pump does start as confirmed by the current draw but does not pump. The discharge line from the oil filter is cool confirming no flow. The oil temp is at design of approx 143F, and the oil filter was recently replaced during winter maintenance. I can cycle the pump numerous times until it finally catches as though it is priming itself and then oil pressure is properly established. Repeated attemts of starting the pump will usually result in a positive oil pressure until the chiller is off over night and attemts to start the next day when the cycle repeats itself. I am thinking that a key may be sheared between the motor and the oil pump gears, any other ideas would be appreciated before we have to open it up.

oil pump

this happens to me when I do not have a tight seal on filter housing. Check gasket on oil filter. They tend to get air locked on R-11 units. Also check your oil pressure regulator. It could be sticking, also our Trane has a strainer that needs to be cleared at the oil regulator. Good luck

This setup has no bypass line externally. The oil pump draws 5.2 amps with no output pressure, and 5.3 amps with pressure, both of these readings are with the chiller off. When the chiller is running the pump draws 3.8 amps. FLA on this pump is 4.8. No prevac and the room temp is around 75F. I also tried raising the oil temp to 150F but with no difference.

Does this chilller have the refrig pump/oil pump?
Either way I would try rebuilding the reg, you can do that without pulling gas. At 0 psi.
You never said how old of a chiller? What are the first three digits of the S#

we just had a similar situation after numerous attempts finally decided to pull pump and motor replaced everything oil had a cloudy look to it installed all new parts it is up and running and a sample of the oil is out for analysis our TRANE machine was a 1999 vintage.

Thanks Lord, I have ordered a rebuild kit for the oil pressure regulator.......am going to try that first. My oil analysis taken last fall indicated the oil was still good. Will post again when the regulator has been rebuilt.

Thought I'd do a follow up after I was sure of the problem was corrected. First the oil pressure regulator was rebuilt but this did not correct the problem. Soooo.....we had to remove the gas and then the pump. Separated the pump from the motor and the drive insert was good. A visual inspection of the pump looked fine. There was a small amount of backlash in the gears but I would not have bet a dime that this was the problem. Decided to change the pump only..........motor was good. Been three weeks now and not one failure.